Method for measuring sound absorption power of a theater chair with a human being seated thereon and a dummy sound absorber

ABSTRACT

There is provided a method for measuring a sound absorption power of a theater chair with a human being seated thereon. The method includes steps of disposing a theater chair which is an object of measurement in a measuring environment; disposing a dummy sound absorber in the theater chair, the dummy sound absorber having a shape in which it is in contact with the theater chair, a sound absorption power and a chair pressing force in such a manner that the dummy sound absorber simulates a human being seated on the theater chair; causing changes in the theater chair which changes are substantially equivalent to a change in the state of the theater chair caused when a human being gets seated on the chair and a change in the sound absorption power of the theater chair caused by seating of the human being thereon; and measuring the sound absorption power of the theater chair. There is also provided a dummy sound absorber used for carrying out this method.

This application is a continuation of application Ser. No. 08/902,907,filed Jul. 29, 1997, now U.S. Pat. No. 6,463,817 which is a continuationof application Ser. No. 08/465,988, filed Jun. 5, 1995, now abandoned,which is a divisional of application Ser. No. 08/129,261, filed Sep. 30,1993, now U.S. Pat. No. 5,465,469.

BACKGROUND OF THE INVENTION

This invention relates to a method for measuring sound absorption powerof a theater (hall) chair with a human being seated thereon and a soundabsorption dummy used for this method and, more particularly, to themethod and dummy which can measure sound absorption capacity of a hallchair in such a state easily and accurately.

A sound absorption characteristic of a chair in a theater or auditorium(hereinafter referred to as “theater chair”) is a very important factorin the acoustic designing of a theater. It has generally been customaryin the past to measure a sound absorption characteristic of a hall chairper se in a state wherein a human being is not seated on the chair. Thesound absorption characteristic of a hall chair should however bemeasured in a state wherein a human being is seated on the chair inquestion.

It has recently been proposed to provide a theater chair with a constantsound absorption power intended to enable an acoustic characteristic ofa hall to remain unchanged between a state wherein a human being isseated on the hall chair and a state wherein he is not seated thereon(e.g., as described in the specification and drawings of JapaneseUtility Model Application No. Hei 4-45924 filed by the assignee of thepresent invention). In designing such a hall chair, it is necessary tomeasure not only the sound absorption characteristics during an unseatedstate but also those during a seated state.

In a case where a sound absorption characteristic of a hall chair duringa seated state is to be measured, a measurement is made under thecondition that a human being is actually seated on the hall chair.

The method according to which the sound absorption characteristic ismeasured with a human being seated on the theater chair however has thefollowing inconveniences:

1. Reliability and reproducability of a measured value are not adequate.Since the posture of the person seated on the hall chair differs fromperson to person and since presence of a human being affects temperatureand humidity of the chamber (hall) in which the measurement is made,these factors cause measurement errors. Further, movement and posture ofa human being and the clothing he wears during the measurement alsoaffect the measurement very much.

2. It is difficult to compare results of the plural measurements witheach other for the reasons described above in 1.

3. The measurement is an unpleasant experience for the human beingseated on the hall chair and this causes the inconvenience describedabove in 1.

4. It is a troublesome task to collect ten to twenty persons to bemeasured at one time.

It is, therefore, an object of the invention to provide a method formeasuring a sound absorption capacity capable of easily and accuratelymeasuring a sound absorption capacity of a hall chair with a human beingseated thereon and provide also a sound absorption dummy used for thismethod.

SUMMARY OF THE INVENTION

A method for measuring a sound absorption power of a theater chair witha human being seated thereon achieving the above described object of theinvention comprises steps of disposing a chair which is an object ofmeasurement in a measuring environment; disposing a dummy sound absorberin the chair, said dummy sound absorber having a shape in which it is incontact with the chair, a sound absorption power and a chair pressingforce in such a manner that the dummy sound absorber simulates a humanbeing seated on the chair; causing changes in the chair which changesare substantially equivalent to the changes in the state of the chaircaused when a human being gets seated on the chair and a change in thesound absorption power of the chair caused by seating of the human beingthereon; and measuring the sound absorption power of the chair.

A dummy sound absorber used for measuring a sound absorption power of achair with a human being seated thereon comprises a chair contactingportion having a shape which is substantially equivalent.to the shape ofportions of a human being which are in contact with a seat and a back ofthe chair when the human being is seated on the chair, sound absorptionpower generation means for generating a sound absorption power which issubstantially equivalent to the sound absorption power formed by a humanbody when the human being wearing clothing is seated on the chair, andpressing force generation means for generating a weight or a forceequivalent to the weight for imparting a pressing force which issubstantially equivalent to a pressing force imparted by the human bodyto the seat surface and the back of the chair when the human being isseated on the chair.

According to the invention, measurement is performed by disposing in thechair a dummy sound absorber having a shape in which it is in contactwith the chair, a sound absorption power and a chair pressing force insuch a manner that the dummy sound absorber simulates a human beingseated on the chair and, hence, results of measurement which aresubstantially equivalent to those of measurement conducted when a humanbeing is seated on the chair can be obtained. Moreover, since theseating condition can be standardized and an immobile posture can bemaintained, as compared to a case where a human being is seated on thechair, and since the disposition of the dummy in no way affectstemperature and humidity of the measuring environment, data availablewhen a human being is seated under standard conditions can be obtained.As a result, reliability and reproducability of the measurement of thesound absorption power can be maintained. Further, data of chairs ofdifferent specifications can be compared with each other with accuracy.Furthermore, since it is not necessary to collect many persons to bemeasured, the measurement can be made at any time and with great ease.

Further, according to the invention, in designing a theater chair with aconstant sound absorption power, difference in the acousticcharacteristic of the theater between the seated state and the emptystate can be minimized by measuring the sound absorption power in theseated state and that in the empty state and designing the theater chairon the basis of the result of the measurement.

Preferred embodiments of the invention will now be described withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings,

FIGS. 1A and 1B are diagrams showing an embodiment of the method formeasuring a sound absorption power according to the invention;

FIG. 2 is a block diagram showing a specific example of an operationunit 26 shown in FIG. 1A;

FIG. 3 is a graph showing an example of reverberation curves stored in achart table ROM 130 of FIG. 2;

FIG. 4 is a graph showing results of measurement according to the methodof FIGS. 1A and 1B;

FIGS. 5A and 5B are graphs showing results of measurement according tothe method of FIGS. 1A and 1B;

FIG. 6 is a graph showing results of measurement according to the methodof FIGS. 1A and 1B;

FIGS. 7A and 7B are graphs showing results of measurement according tothe method of FIGS. 1A and 1B;

FIGS. 8A and 8B are diagrams showing methods of measuring influence ofweight on the sound absorption capacity;

FIG. 9 is a graph showing results of measurement according to themethods of FIGS. 8A and 8B;

FIG. 10 is a graph showing results of measurement according to themethod of FIGS. 1A and 1B;

FIGS. 11A and 11B are diagrams showing an embodiment of the dummy soundabsorber according to the invention in which FIG. 11A is a front viewand FIG. 11B is a side view;

FIG. 12 is a graph showing results of measurement of a sound absorptionpower by the dummy of FIGS. 11A and 11B;

FIGS. 13A and 13B are diagrams showing another example of the pressingforce generation means;

FIGS. 14A and 14B are diagrams showing another example of the pressingforce generation means;

FIGS. 15A and 15B are diagrams showing examples of detachable weights;

FIGS. 16A and 16B are diagrams showing another embodiment of the soundabsorption dummy according to the invention.

FIG. 17 is a view showing a specific example of the theater chair with aconstant absorption power;

FIG. 18 is a view showing the state of use of the chair;

FIG. 19 is a view showing another specific example of the theater chairwith a constant absorption power; and

FIG. 20 is a view showing the state of use of the chair.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1A and 1B show an embodiment of a device for carrying out themethod for measuring a sound absorption capacity in which FIG. 1A showsa reverberation chamber 10 in a plan view and FIG. 1B is an elevationalview as viewed in the direction of lines A—A. In this embodiment,“PLD/Deep-well method” is employed. According to this method, the randomincident sound absorption coefficient α₀₀ can be measured rationallywithout being affected by dispersion condition and an area effect (edgeeffect) of the reverberation chamber. In this method, the area effect isremoved by enclosing, in a reverberation chamber, a sound absorbingsample with an acrylic plate (deep-well) which is higher than the soundabsorbing sample, and non-diffused condition which is thereby enhancedis measured quantitatively as a curvature of a reverberationcharacteristic curve. The random incident sound absorption rate α₀₀ ismeasured accurately by estimating (by PLD correction) an average soundabsorption capacity of Sabine on the basis of the initial attenuationrate of the non-dispersion condition. As regards the theory of theDeep-well method, reference is made to Technical Report vol. 91, No.329, November 1991, EA91-69 of Electronic Information CommunicationSociety of Japan as well as Japanese Patent Application Laid-open No.Hei 3-276031.

In the embodiment of FIGS. 1A and 1B, parameters of the reverberationchamber 10 (the measuring environment) are determined, for example, asfollows:

capacity=267.6 m³

surface area=249.2 m²

floor area=34.3 m²

f_(min)=115 Hz

In the reverberation chamber 10 is provided a well 12 and in this well12, there are provided, as best seen in FIG. 1B, a plurality of hallchairs 14 which are objects of measurement. In each hall chair 14 isdisposed a sound absorption dummy 16 in a seated state. The soundabsorption dummy is constructed so that it has a shape in which it is incontact with the hall chair 14, a sound absorption capacity and a chairpressing force in such a manner that the dummy 16 simulates a humanbeing seated on the hall chair 14. By this arrangement, changes, whichare substantially equivalent to a change in the state (shape) of thehall chair 14 caused when a human being is seated on the hall chair 14and to a change in the sound absorption capacity of the hall chair 14caused by the seating of the human being thereon, are brought about inthe hall chair 14 and thereby the sound absorption capacity of the hallchair 14 can be measured under these conditions.

In FIG. 1A, a short sound generation unit generates a tone burst(impulsive sound) as the sound source used for the measurement and thetone burst is sounded from a loudspeaker 20 provided in thereverberation chamber 10. A microphone 22 is provided in thereverberation chamber 10 for collecting or picking up sound waves whichare propagated from the loudspeaker 20 and reflected from the walls ofthe reverberation chamber 10.

The sound collected by the microphone 22 is transmitted to an operationunit 26 through an amplifier 24. The operation unit performs measurementof a sound absorption capacity for each frequency. Results of themeasurement such as a sound absorption power and a reverberation curve,are supplied to a display and recording unit 28 for display on a CRTscreen and printing out of the results. A specific example of theoperation unit 26 is shown in FIG. 2. This operation unit is one inwhich spatial ensemble average of reverberation when the sound source(tone burst) is cut off is calculated with respect to both a case wherethe reverberation chamber 10 is empty and a case where the theater chair14 and the Deep-well 12 are arranged in the chamber 10, the degree ofcurvature is obtained by comparing the respective reverberationwaveforms with theoretical values, reverberation times T0 and T1 to theattenuation rate of linear attenuation in a perfect diffusion soundfield is obtained from the degree of curvature, and the sound absorptionpower is calculated on the basis of T0 and T1.

In FIG. 2, in the state before generation of an impulse, noise n(x) inthe reverberation chamber 10 is collected by any of microphones 22-1 to22-n and, after being converted to a digital signal by ananalog-to-digital converter 107 through an amplifier 24, is squared by asquaring circuit 108. The output n²(x) is cumulatively added by anaccumulator 109 to obtain ∫ n²(x) dx. This result of multiplication isdivided by time of accumulation τ by a division circuit 125, through aregister 124, to obtain an average value of squaring of the noise n(x),i.e., result of squaring value n_(eff) of the effective value of thenoise n(x).

Then, before generation of a first impulsive sound from a loudspeaker20, a common terminal 105-COM of a switch 105 is connected to a contact105-1, and the accumulator 109, a RAM 114 and a register 112 arecleared. Upon generation of impulsive sound from the loudspeaker 20 by atone burst generator 18, the microphone 22-1 collects a sum(R(x)=rl(x)+n(x)) of this impulse rl(x) and the noise n(x) in thereverberation chamber 10. This sum R(x) is converted to a digital signalby an analog-to-digital converter 107 and squared by the squaringcircuit 108 to provide R²(x). The square n²(x) of the effective value ofthe noise n(x) is subtracted from R²(x) to provide R²(x)-n² _(eff) bysubtraction circuit 123. This result of the subtraction is cumulativelyadded by an accumulator 109 to provide ∫^(t) ₀ [R²(x)-n² _(eff)] dx. Theresult of the accumulation is successively applied to a register 110 ata predetermined timing. Output of the register 110 is added to output ofthe register 112 by the addition circuit 111. The result of the additionis stored at a predetermined address in the RAM 114 and also is appliedto a register 113.

In this case, each time a predetermined period of time has elapsed fromthe start of the measurement, the contents of the accumulator 109 areapplied to the register 110. At a first timing, data (S1-1) in theaccumulator 109 is applied to the register 110.

Simultaneously, the data of address “1” of the RAM 114 is applied to theregister 112. At this time, the RAM 114 is cleared and, accordingly, thevalue applied to the register 112 is “0”. The data in the register 112and the data “S1-1” in the register 110 are added together by theaddition circuit 111 [i.e., (S1-1)+0]. The added data “S1-1” isrewritten at address “1” in the RAM 114 and also applied to a register113. At the next timing, data (S1-2) of the accumulator 109 is appliedto the register 110 and, thereupon, data (=“0”) at address “2” in theRAM 114 is applied to the register 112 and addition of [(S1-2)+0] ismade by the addition circuit 111. The result (S1-2) of the addition iswritten at address “2” in the RAM 114 and applied to the register 113.Subsequently, writing in the RAM 114 and the register 113 is made in thesame manner to the end of the accumulation of the accumulator 109. Thatis, at a time point when writing at the end of the accumulation has beencompleted, data “S1-1” is written at address “1”, “S1-2” at address “2”,“S1-3” at address “3” . . . , “S1-m” at address “m” whereas data “S1-m”is written in the register 113.

In this manner, upon completion of the collection of impulse responserl(x) by the microphone 22-1, the common terminal 105-COM of the switch105 is connected to a contact 105-2 and the accumulator 109 is cleared.Second impulse response r2(x) is sequentially processed in a similarmanner to the above described processing from the loudspeaker 20.

Upon inputting of a first accumulated value (S2-1) in the register 110,data at address “1” in the RAM 114 (the data S1-1 is stored by the abovedescribed processing) is applied to the register 112 and an addition of[S2-1+S1-1] is made by the addition circuit 111. The result of theaddition is applied again at address “1” of the RAM 114 and the register113. Subsequently, in a similar manner, accumulated value of impulseresponse r2(x) is sequentially added to the data of the RAM 114 and thefollowing data are sequentially stored in the respective addresses ofthe RAM 114:

at address 1: [S1-1+S2-1]

at address 2: [S1-2+S2-2]

at address 3: [S1-3+S2-3]

.

.

.

.

at address m: [S1-m+S2-m]

Then, impulse responses r3(x), r4(x), . . . , rn(x) are sequentiallycollected by the microphones 22-3, 22-4 . . . and 22-n and theiraccumulated values are sequentially added to the contents of the RAM114. Therefore, when all of the processing of n impulse responses r1(x),r2(x), . . . , rn(x) has been completed, the data of the RAM 114 is asfollows:

at address 1: [S1-1+S2-1+ . . . Sn-1=TS1]

at address 2: [S1-2+S2-2+ . . . Sn-2=TS2]

.

.

.

at address m: [S1-m+S2-m+ . . . Sn-m=TSm]

Thus, data TSm is written in the register 113.

The data TSm of the register 113 is applied to one of the inputterminals of a subtraction circuit 115 through a latch circuit 116. Onthe other hand, the data in the RAM 114 is sequentially read out andsupplied to the other input terminal of the subtraction circuit 115. Inthe subtraction circuit 115, therefore, the following operations aresequentially performed:

[TSm−TS1=Z1], [TSm−TS2=Z2] . . . [TSm−TSm=Zm]

The result Z1 to Zm of this operation represents spatial ensembleaverage {<S²(t)>}_(NO).

This space aggregation average {<S²(t)>}_(NO) includes an error due todeficiency of diffusion in a sound field and, therefore, a processingfor eliminating this error is performed. More specifically, since thecurve of the spatial ensemble average {<S²(t)>}_(NO) reflects deficiencyof diffusion in the sound field in the attenuation process,it isnecessary to obtain sound absorption capacity in a perfectly diffusedsound field by compensating for lack of diffusion (deficiency indiffusion) by employing a parameter indicating the degree of thecurvature. An operation for this purpose will now be described.

The result of operation Z1 to Zm of the above described spatial ensembleaverage is logarithmically compressed by a ROM 117 to obtainreverberation characteristic curve 10 log {<S²(t)>}_(NO). Thisreverberation curve is applied to an interface 118 to be timewisedisplayed on and/or recorded into a display/recording unit 119.

In a chart table ROM 130, plural curve data corresponding to theoreticalvalues of reverberation curves are stored. The theoretical values areexpressed by

L _(N)(t)=−4.34(N−1)ln(1+{overscore (a)}*t/N)

where N represents the number of independent points which can bedetermined on a specimen (i.e., chair 14) and which constitutes an indexconcerning the degree of the curvature which indicates that the curve isnearer to a straight line as this index becomes greater. Assuming thatthe area of the specimen is S and the reverberation wave length is λ, Ncan be approximated by S/(λ/2)²; {overscore (a)} represents an indexconcerning the attenuation rate of an initial portion of thereverberation curve; and t represents time.

As parameter of the curve of the theoretical value L_(N)(t), thefollowing t₃₀ (time until the reverberation curve attenuates by 30 dB)and Q₃₀ (the degree of curvature of the reverberation curve) are used:

t ₃₀=(N(exp(30/(4.34(N−1))−1)))/{overscore (a)}

Q ₃₀=30/(N−1).

By way of example, curves of theoretical value L_(N)(t) in the case oft₃₀=31.0 ms are shown in FIG. 3.

A comparison and operation circuit 131 compares a reverberation curveprovided by the ROM 117 with the curves stored in the chart table ROM130 and selects the nearest curve in the stored curve in the chart tableROM 130. Then, the circuit 131 calculates reverberation time T_(NO) fromthe following formula by using Q₃₀ and t₃₀ of the selected curve:

T _(NO)=(13.8 Q ₃₀ ·t ₃₀)/(30(exp(Q ₃₀/4.34)−1)).

Further, on the basis of this T_(NO) obtained, reverberation time T₀₀corresponding to the attenuation rate of linear attenuation in theperfectly diffused sound field (i.e., deficiency in diffusion has beeneliminated) can be calculated by the following equation:

T₀₀=(N−1)T _(NO) /N.

This reverberation time T₀₀ is calculated with respect to a case wherethe reverberation chamber 10 is empty and also a case where the hallchair 14 and well 12 are provided in the reverberation chamber 10, andthen respective calculated reverberation times are designated by T₀ andT₁. The sound absorption capacity of the hall chair 14 can be calculatedfrom the following formula:

a ₀₀=(55.3V/(c*n))(1/T1−1/TO)

where V represents the volume of the reverberation chamber 10, nrepresents the number of hall chairs 14 and c represents the velocity ofsound.

Description will now be made about the sound absorption dummy 16 usedfor the method shown in FIGS. 1A and 1B. First of all, results ofmeasuring characteristics under the condition that a human being isactually seated on the hall chair 14 by the measuring device shown inFIGS. 1A and 1B will be described. The measurement was conducted byusing two different hall chairs (hereinafter referred to as “chair A”and “chair B”) having different sizes and specifications as describedbelow. Chair A (four chair A's are arranged in two lines)

back: plywood 25t+urethane 30t to 100t

seat: plywood 20t+urethane 20t

 (Width)×(Depth)×(Height)=500×685×850 (in mm)

Chair B (five chair B's are arranged in two lines)

back: plywood 21t+GW25t, 80 Kg/m³

seat: plywood 21t+GW25t, 80 Kg/m³

(Width)×(Depth)×(height)=550×640×900 (in mm).

Adults wearing summer clothing (e.g., a sport shirt with half-lengthsleeves or similar clothing) or winter clothing (the summer clothingplus outfit for protection against the cold) participated in themeasurement.

Results of the measurement are shown in FIG. 4. Despite the greatdifferences in the size and specification between chair A and chair B,the sound absorption power does not differ very much between chair A andchair B when no human being is seated thereon. When the human being isseated thereon, there is a difference ranging from 0.06 to 0.08(m²/chair) between chair A and chair B at frequencies over 250 Hz, i.e.,at 500 Hz, 1 kHz, 2 kHz and 4 kHz, depending upon the clothing worn bythe human being. At 250 Hz, there is a great difference between chair Aand chair B depending upon the clothing worn, indicating that the soundabsorption characteristic sometimes differs when a human being is seatedin 2 chairs having similar sound absorption characteristics.

FIGS. 5A and 5B show results of measurement of the sound absorptionpower of the human being only and that of chair A or chair B only.Difference between the arithmetic sum of the sound absorption power ofthe human being and the sound absorption power of the chair A or B(indicated by the dotted line) represents decrease in the soundabsorption power due to close contact of the human's body with thechair. This difference differs greatly at 250 Hz depending upon the typeof the chair. Since chair A has a relatively thick back (30-100 mm), thesound absorption power seems to decrease substantially due tocompression of the back of the chair when the human being is seated onchair A as will be described later. On the other hand, the soundabsorption power of chair B at 250 Hz when the human being is seatedthereon is close to the arithmetic sum of the sound absorption power ofthe chair only and that of the human being only.

The above results of measurement in the case where the human being isactually seated on the chair indicate that consideration should be givenboth to the dummy sound absorber 16 only and to the state wherein thedummy sound absorber 16 is seated on the chair. As requirements for thedummy sound absorber 16, the following four factors should beconsidered:

(1) Size and power: The dummy should simulate an average adult person insize and shape.

(2) Material: The material of the dummy should be so selected that thesurface of the dummy produces a sound absorption capacity which issubstantially equivalent to what an adult person wearing clothing willproduce.

(3) weight: The dummy should have a weight sufficient for compressingthe cushion of the chair to substantially the same degree as an adultperson does.

(4) Mobility: The dummy should be in a close contact posture with thechair.

Initially, for achieving the above factors (1) and (2), a dummy soundabsorber was made of foamed polyurethane and partially finished withfoamed polyurethane (having weight of about 5 kg:) and the soundabsorption power of this dummy only was measured. For achievinginfluence of the sound absorption characteristic of the chair, themeasurement was conducted with the dummy seated on a round chair whichhardly has any sound absorption power. Results of the measurement areshown with the sound absorption power of the human being only in FIG. 6.This dummy exhibits a sound absorption power which lies midway betweenthe human being wearing summer clothing and the human being wearingwinter clothing and therefore is preferable as a standard dummy soundabsorber.

Then, measurement was conducted with this dummy being seated on chair Aand chair B respectively. Results of the measurement are shown in FIGS.7A and 7B. As in FIG. 6, the sound absorption power of the dummy beingseated on chair A or B almost lies midway between that of the humanbeing wearing summer clothing and that of the human being wearing winterclothing. At 250 Hz only, however, the dummy sound absorber exhibits agreater sound absorption power and, therefore, the dummy is still notsufficient. This effect seems to be attributable to the fact that theweight of the dummy sound absorber (about 5 kg) is different from thatof the human being.

Accordingly, having regard to the above factor (3), influence of weightwas examined. For this purpose, as shown in FIGS. 8A and 8B, measurementwas conducted with respect to a case (a) where eight cushions 30 eachconstituting the back of the chair are disposed on a floor 31 of thewell 12 in the reverberation chamber 10 and an acrylic plate 32 only isplaced around cushion 30 and a case (b) where a weight 34 (about 20 kgwhich corresponds to the weight of the trunk of an adult male) is placedon top of the acrylic plate 32 to compress the cushion 30. Results ofthe measurement are shown in FIG. 9. In the case that there is no weight34, the sound absorption capacity exhibits a peak value at 250 Hz.Whereas, when the cushion 30 is compressed, this peak value no longerexists, indicating the importance of the above factor (3). This is alsoconsidered to be a main reason for decrease in the sound absorptionpower in the case of chair A shown in FIG. 5A.

Then, having regard to the above factor (4), influence of the seatingposition of a dummy sound absorber (one which materializes the abovefactor (1) and (2) having weight of about 5 kg) was examined. Results ofthe measurement are shown in FIG. 10. These results reveal that thesound absorption characteristic changes as the seating posture changesfrom a standard state in which both the back and thighs of the dummy arein close contact with the chair (indicated by the symbol ↑ in thefigure), to a state in which the back of the dummy is not in contactwith the chair (indicated by the symbol ▪ in the figure), and further toa state in which the dummy has moved forward and is seated on the frontend portion of the seat of the chair (indicated by the symbol  in thefigure). From this, it has been found necessary to always keep the sameseating posture of the dummy. Since persons normally are seated ontheater chairs in the posture in which they are in close contact withthe theater chair, it is desirable to measure the sound absorption powerwith the dummy sound absorber seated in this posture.

An embodiment of a dummy sound absorber satisfying the above factors (1)to (4) is shown in FIGS. 11A and 11B. This dummy sound absorber 16 ismade of foamed polystyrene used as a non-sound absorbing material andhas the shape of a human being. That is, the dummy 16 has a head 42, atrunk 44, upper arms 46, forearms 48, thighs 50 and legs 52. The upperarms 46 and the forearms 48 may be provided only when the elbow seats 15of a chair 14 are made of sound absorbing cushions. Sizes of the dummy16 are determined to standard sizes of an adult male, i.e, the height ofhead and trunk is 90 cm, the height of legs is 41 cm, the width ofshoulders is 40 cm and the width of hips in the seated position is 34 cmfor an average Japanese adult male. The entire surface of the dummy iscovered with a porous sound constitutes the sound absorption power of ahuman being per se. The dummy 16 is covered with a cloth which is put onthe porous sound absorbing material 36.

Movable portions are provided in the dummy 16 so that it can assume aseated posture. More specifically, joints 54, 56, 58, 60 and 62 areprovided in the shoulders, elbows, hips, knees and ankles. A flexiblemember 66, such as a metal wire which can flexibly change its shape, isburied in the back portion of the trunk 44 in such a manner that theback of the dummy 16 can be brought into close contact with the back 68of the hall chair 14. A flexible member 67 is also buried in the neck ofthe dummy 16 so that he inclination of the head 42 can be adjustedfreely.

A weight 72 is buried in the trunk 44 and a weight 74 is buried in thethighs 50. The weights 72 and 74 constituting the pressing forcegeneration means impart the cushions of the back 68 and a seat 70 of thechair 14 with loads which are substantially equivalent to loads impartedby the human being when he is seated on the chair 14. The weights 72 and74 may be made, for example, of iron blocks or iron plates. Assuming,for example, that the weight of the human being seated on the chair 14is 58.8 kg and that the ratio of the weight of the trunk of the humanbeing to the weight of his whole body is 0.54, weight W1 of the weightin the trunk 44 is determined, for example, to W1=58.8 kg×0.54=32 kg.for average Japanese men.

Assuming also that the ratio of the weight of one thigh of the humanbeing to the weight of his whole body is, for example, 0.07, weight W2of the weight 74 in the thigh 50 is determined, for example, to W2=58.8kg×0.07=4 kg.

By adjusting the angles of the joints 54, 56, 58, 60 and 62 and thebending sates of the flexible members 66 and 67 of the dummy 16, thedummy 16 can be seated on the chair 14. In the seated state, a back 44 aof the trunk 44 which constitutes a part of the chair contacting portionis brought into close contact with the back 68, and the lower surfaces50 a of the thighs 50 which constitute also a part of the chaircontacting portion are brought into close contact with the seat 70. Theweights 72 and 74 act to impart the cushions of the back 68 and the seat70 with a pressing force which is substantially equivalent to thepressing force imparted when the human being is seated on the chair 14.By this arrangement, measurement of the sound absorption power can beeffected in substantially the same conditions as when the human being isactually seated on the hall chair 14.

Results of measurement made by the method described with reference toFIGS. 1A and 1B with the dummy of FIGS. 11A and 11B seated on chair A aswell as results of measurement made when the human being is actuallyseated on chair A are shown in FIG. 12. These results indicate that thesound absorption capacity of the dummy 16 lies midway between the soundabsorption capacity of a human being wearing summer clothing and thesound absorption capacity of a human being wearing winter clothing and,therefore, is preferable as a standard dummy sound absorber.

In the above described embodiment, weights are buried in the dummy asthe pressing force generation means. There may however be a case whereit is inconvenient to carry and handle a dummy sound absorber having aweight equivalent to that of a human body. For coping with such a case,as shown in FIG. 13A, the pressing force may be generated by bindingportions such as the trunk and thighs of a dummy sound absorber 16 bymeans of wires 80 or the like. In this case, a fastener 82 shown in FIG.13B or like fastening means may be used. By adjusting the bindingcondition of the wires 80 by operating the fastener 82, the pressingforce can be adjusted to a desired value. The fastener 82 may beprovided on the dummy 16 as one of its component parts. In FIGS. 13A and13B and subsequent figures, the same component parts as those in FIGS.11A and 11B are designated by the same reference characters anddescription thereof will be omitted.

Alternatively, as shown in FIG. 14A, iron plates 86 having proper areasmay be buried in the dummy 16 and the pressing force may be generated byattracting these iron plates 86 by magnets 88 provided outside of thedummy 16. If an electromagnet is used as the magnet 88 as shown in FIG.14B, the magnetic attraction can be determined to a desired value byoperating a magnetic attraction adjusting device 90.

In the case of using weights as the pressing force generation means, itbecomes easier to carry the dummy by constructing the dummy so that, asshown in FIGS. 15A and 15B,

The foregoing embodiments have been described with reference to themeasurement of sound absorption power of the existing hall chair. Theinvention can be effectively applied to the designing of a theater chairwith a constant sound absorption power capable of maintaining acousticcharacteristics of a hall unchanged.

As a characteristic of a theater chair with a constant sound absorptionpower, the chair is required to have a small sound absorption power andhave little change in sound absorption power by seating thereon. Morespecifically, the theater chair with a constant sound absorption poweris a chair which can be defined in the following manner:

A theater chair with a constant sound absorption power is a chair whosesound absorption power per one chair when the chair is empty obtained bymeasuring by the random incident sound absorption coefficient measuringmethod on the assumption that chairs which are arranged in parallel on aflat floor in such a manner that geometrical relations of these chairsto one another is substantially the same as that of chairs arranged in atheater are a flat sound absorption material, and whose total “soundabsorption power” per one chair and one human being when he is seated onthe chair determined on the condition that an adult male wearingbetween-season wear (meaning a human body having weight of about 65 kgand whose sound absorption power is about 0.3 m² (metersabine) at afrequency of 500 Hz when seated alone) is seated on the chair in anatural posture or on a similar condition are respectively 0.4 m²(metersabine) or below and, weights 72 and 74 can be inserted into anddetached from the trunk 44 and thighs 50 of the dummy.

In the above described embodiment, the main body of the sound absorptiondummy 16 is made of foamed polystyrene. Alternatively, the main body ofthe dummy 16 may be made of other non-sound absorbing material such assilicon or plaster. When plaster, which is a relatively heavy material,is used for making the main body, the use of the weights may beeliminated or reduced.

In the above described embodiment, the entire surface of the dummy 16 iscovered with a sound absorbing material. Alternatively, the dummy 16 maybe covered with the sound absorbing material only in a portion which isexposed outside in the seated state of the dummy 16. If the main body ofthe dummy 16 is made of a material having a sound absorption capacitywhich is close to that of a human being, it will not be necessary tocover the main body with a sound absorbing material.

In the above described embodiment, the sound absorption dummy 16simulating a human body is used. However, portions of the dummy which donot influence results of the measurement of the sound absorptioncapacity very much may be omitted. It is essential that the dummy soundabsorber should satisfy the above described factors (1) to (4) and, forthis purpose, as shown in FIGS. 16A and 16B, a dummy sound absorber 16′may be constructed of only a portion 44′ corresponding to a trunk and aportion 50′ corresponding to the thighs. when frequency bands from 125Hz to 4 kHz are divided by one octave band and sound absorption power ofan empty chair and that of a seated chair are measured, change betweenthe empty chair and the seated chair in each band is 10% or below ofsound absorption power of the empty chair.

As to these values of sound absorption power, reference should be madeto the following literature:

(1) “ACOUSTICS” Leo L. Beranke, Pages 300-301, McGraw-Hill Book Company,1954.

(2) “Acoustic Designing in Architecture”, Vern O. Knudsen and Cyril M.Harris, Pages 170-175, published by the American Institute of Physicsfor the Acoustic Society of America, 1980.

(3) “Reverberation Time Difference Limeus in the Simulated Sound Fieldof an Actual Hall”, Y. Tahara and T. Miyajima, Pages 527 and 528,published by The Acoustical Society of Japan, March 1988.

A specific example of the theater chair with a constant sound absorbingpower satisfying the above described definition will be described. Thistheater chair is constructed in such a manner that sound absorptionpower concentrates on the seat and the back which are concealed byseating of a human being and the chair has a third sound absorptionsurface which is exposed when the human being leaves the chair. FIG. 17shows this example.

In FIG. 17, the chair has a support 220. The support 220 has a pair ofside plates 222 which have elbow rests 221 at the top end thereof andare fixed to the floor in an upright state, a back plate 223 whichbridges the rear edges of the side plates 222, and a lower plate 224which is disposed in a horizontal posture and fixed to the side plates222 at their central portions. These side plates 222, back plate 223 andlower plate 224 are all made of a material which reflects sound.

A cushion 225 made of a material having elasticity and sound absorptionpower such as polyurethane or glass wool is fixedly secured on the frontsurface of the back plate 223 and a decorative cloth 226 is provided onthe surface of the cushion 225 to form a back rest 227. Similarly, afixed seat 230 including a cushion 228 and cloth 229 is provided on theupper surface of the lower plate 224. The surfaces of the back rest 227and a fixed seat section 230 have sound absorption power. The fixed seatsection 230 may be constructed as a sound absorbing trap structure toimprove the sound absorption power.

On the other hand, there is provided on the fixed seat section 230 amovable seat section 234 which includes cushions 232 fixed on bothsurfaces of a core 231 and is covered with cloth 233 in its entiresurface. The rear end portion of the movable seat section 234 isrotatably supported by a horizontal shaft 235 which bridges the sideplates 222 in the vicinity of the rear end portion of the fixed seatsection 230. An unillustrated energizing means is provided in themovable seat section 234 and the movable seat section 234 is therebycaused to spring up to a position at which the movable seat section 234does not reach the back rest 227 as shown in the figure when the chairis empty.

On the inside surface of each side plate 222 is formed a sound absorbingsection 236 at a position opposite to the hip and thigh of a human beingin the seated position. The sound absorbing section 236 includes acushion covered with cloth. On the rest of the inside surface of eachside plate 222 is secured a reflective material 237 which reflectssound.

In the theater chair with a constant sound absorption power, when theseat is empty, the movable seat section 234 is supported at the positionwhere the movable seat section 234 has sprung up from the fixed seatsection 230 and therefore the sound absorbing lower surface of themovable seat section 234 and the sound absorbing upper surface of thefixed seat section 230 are exposed so that the sound absorption power ofthe chair as a whole is relatively large. When the human being is seatedon the chair, as shown in FIG. 18, the movable seat section 234 ispressed on the fixed seat section 230 whereby the lower surface of themovable seat section 234 and the upper surface of the fixed seat section230 are closed and the front surface of the back rest 227, the uppersurface of the movable seat section 234 and the sound absorbing section236 of each side plate 222 are covered by the human body. Therefore,relation between sound absorption power B of the chair as a whole in theseated state and sound absorption power A of the chair as a whole in theempty state is expressed by the following equation:

 B=A+(1)−(2)−(3)

where (1) represents sound absorption power of the surface of the humanbeing which is not in contact with the chair and sound absorption powerof the surface of the chair which is not in contact with the human body,(2) represents sound absorption power of a portion of either the backrest 227, movable seat section 234 and sound absorbing section 236 ofthe side plates 222 which portion is not covered by the human body inthe seated state, and (3) represents sound absorption power of portionsof the movable seat section 234 and the fixed seat section 230 which arein abutting contact with each other in the seated state.

Accordingly, by determining the sound absorption power to satisfy therelation (1)=(2)+(3), the acoustic characteristic of the hall both inthe empty state and the seated state can be maintained substantiallyconstant. Particularly in this embodiment, the area and sound absorptionpower of the portion (3) can be set at large values, and then it is easyto realize the relation of (1)=(2)+(3).

In this embodiment, the chair is of a simple construction in which theseat is composed of the fixed seat section 230 and the movable seatsection 234 with the movable seat section 234 being rotatable about thehorizontal shaft and, accordingly, this chair is less expensive and moreaccurate in operation than a conventional chair incorporated a slidableshield plate. Besides,the chair of this embodiment has less restrictionto the configuration of the back rest 227 and the seat section 230 and,therefore, a shape such as one having many curved surfaces can be easilyadopted. Thus, the chair of this embodiment has a large degree offreedom in design. Further, since the movable seat section 234 can bemaintained in the sprung up position in the empty state, a cushioneffect can be obtained by the rotation of the movable seat section 234when the human being sits on the chair and this gives comfort to thesitting human being.

FIG. 19 shows another example of a theater chair with a constant soundabsorption power. In this example, a lower plate 240 and a fixed seatsection 241 have a smaller width in the fore and aft direction than theabove described embodiment of FIG. 17. In this embodiment, the movableseat section 242 is supported rotatably on a horizontal shaft 243 whichbridges side plates 222 at their front central portions. The movableseat section 242 includes a sound reflecting plate-like core 244 havinga sound reflecting projection 244A in the lower front end portion, acushion 245 and cloth 246 attached to the core 244 excepting theprojection 244A. The movable seat section 242 is provided withunillustrated energizing means so that the movable seat section 242 iscaused to spring up to an upright position in the empty state whereas,in the seated state, the movable seat section 242 is rotated rearwardlyas shown in FIG. 20 with the lower surface of the rear end portion ofthe movable seat section.242 being brought into close contact with theupper surface of the fixed seat section 241. The other portions are thesame as or similar to the chair shown in FIG. 17.

In the chair of FIG. 19, a sound absorption power adjusting effectsimilar to that of the chair of FIG. 17 can be obtained. Moreover, sincethe movable seat section is rotated rearwardly, the human being can siton the chair by just standing in front of the chair and then sittingdown and, therefore, the movable seat section 242 can be rotatedsmoothly without using the human hand.

Further, in this chair, the movable seat section 242 erects uprightlyalong the front edge of the side plates 222 in the empty state and,therefore, a broader space can be provided between one chair and anotherchair in front in the hall.

What is claimed is:
 1. A dummy sound absorber used for measuring a sound absorption power of a chair with a human being seated thereon comprising: a chair contacting portion having a shape which is substantially equivalent to a shape of portions of a human being which are in contact with a seat and a back of the chair when the human being is seated on the chair; sound absorption power generation means for generating a sound absorption power which is substantially equivalent to a sound absorption power formed by a human body when the human being wearing clothing is seated on the chair; and pressing force generation means for generating a weight or a force equivalent to the weight for imparting a pressing force which is substantially equivalent to a pressing force imparted by the human body to the seat surface and the back of the chair when the human being is seated on the chair.
 2. A dummy sound absorber as defined in claim 1 wherein a main body of said dummy sound absorber is made of a non-sound absorbing material and said sound absorption power generation means comprises a sound absorbing material covering the main body of the dummy sound absorber.
 3. A dummy sound absorber as defined in claim 1 Wherein said pressing force generation means comprises a weight buried in the dummy.
 4. A dummy sound absorber as defined in claim 3 wherein said weight is detachable from the dummy sound absorber.
 5. A dummy sound absorber as defined in claim 1 wherein said pressing generation means comprises a wire for binding a part of the dummy sound absorber to the chair and fastening means for adjusting a binding force of the wire.
 6. A dummy sound absorber as defined in claim 1 wherein said pressing force generation means comprises an iron plate buried in the dummy sound absorber and magnet means provided outside of the dummy sound absorber for attracting the iron plate.
 7. A dummy sound absorber as defined in claim 6 wherein said magnet means comprises an electromagnet and means for variably adjusting the magnetic attraction of the electromagnet.
 8. A method for making a chair comprising the steps of: disposing a chair to be evaluated in a measuring environment; disposing a dummy sound absorber in the chair, the dummy sound absorber having a shape in which the dummy sound absorber is in contact with the chair, a sound absorption power and a force pressing the chair in such a manner that the absorber simulates an actual human being seated on said chair; causing changes in the chair which changes are substantially equivalent to a change in a state of said chair when a human being gets seated on the chair and a change in the sound absorption power of the chair caused by seating of the human being thereon; measuring the sound absorption power of the chair; and controlling a sound absorption power of the chair on a basis of a result of a measurement.
 9. A dummy sound absorber used for measuring a sound absorption power of a chair, having at least one of a seat and a back, with a human seated thereon, the dummy sound absorber comprising: a chair contacting portion having a shape substantially equivalent to that of portions of a human being, the chair contacting portion contacting the at least one of the seat and the back portion of the chair, when the dummy is seated in the chair; sound absorption power generation means for generating a sound absorption power substantially equivalent to a second sound absorption power generated by a human body wearing a predetermined type and amount of clothing and when seated in the chair; and pressing force generation means for generating an adjustable pressure against the at least one of the seat and the back of the chair, wherein the pressure is substantially equivalent to a second pressure that a human being would impart.
 10. The dummy sound absorber of claim 9, wherein the dummy sound absorber comprises a non-sound absorbing material and the sound absorption power generation means comprises a sound absorbing material covering the dummy sound absorber.
 11. The dummy sound absorber of claim 9, wherein said pressing force generation means comprises a weight buried in the dummy sound absorber.
 12. The dummy sound absorber of claim 11, wherein said weight is detachable from the dummy sound absorber.
 13. The dummy sound absorber of claim 9, wherein said pressing force generation means comprises a wire for binding a part of the dummy sound absorber to the chair and fastening means for adjusting a binding force of the wire.
 14. A dummy sound absorber used for measuring a sound absorption power of a chair with a human being seated thereon, comprising: a plurality of rigid members, at least one member having a shape substantially equivalent to that of a portion of a human being, and at least one member having a weight for generating an adjustable pressure against a portion of the chair, wherein the pressure is substantially equivalent to a second pressure that a human being would impart; and sound absorption power generation means for generating a sound absorption power substantially equivalent to a second sound absorption power generated by a human body wearing a predetermined type and amount of clothing and when seated in the chair.
 15. A dummy sound absorber used for measuring a sound absorption power of a chair with a human being seated thereon, comprising: a plurality of rigid members, at least one member having a shape substantially equivalent to that of a portion of a human being, the plurality of rigid members being adjustably joined to each other and imparting a pressing force on the chair when the dummy is seated thereon, the pressing force being adjustable by adjusting relative positions of the adjustable joined rigid members, wherein the pressing force is substantially equivalent to a second pressing force that a human being would impart; and sound absorption power generation means for generating a sound absorption power substantially equivalent to a second sound absorption power generated by a human body wearing a predetermined type and amount of clothing and when seated in the chair.
 16. A dummy sound absorber comprising: an outer surface having a shape that is at least in part substantially equivalent to a shape of portions of a human body having a predetermined shape and positioning, wherein the outer surface generates a sound absorption power which is substantially equivalent to a second sound absorption power generated by the human body having a predetermined sound absorption power; and a force generator that causes the dummy sound absorber to impart an adjustable pressing force on an object, wherein the pressing force is substantially equivalent to a second pressing force that a human being would impart. 